Requirement of the T cell antigen receptor occupancy for the target cell lysis by cytolytic T lymphocytes

We have constructed a bivalent bifunctional F(ab)2 fragment with binding specificity for a V beta 8 T cell antigen receptor and human tumor-associated antigen. Using the bifunctional antibody to focus cytolytic activity of mouse CTL to a human carcinoma cell line and anti-V beta 8 TCR Fab' as a competitor, we demonstrate that only a small percentage (-0.5%) of the TCR engaging on the target molecule is sufficient to deliver a lytic signal to the target cells.